Echo Suppression Research Articles

Effect of spectral overlap on the echo suppression threshold for single reflection conditions

In performing arts venues, the spectra of direct and reflected sound at a receiving location differ, due to seat dip effect, diffusive and absorptive surfaces, and source directivity. This paper examines the influence of differing lead and lag spectral contents on echo suppression threshold. The results indicate, that for a highpass filtered direct sound and a broadband reflection, attenuation of low frequencies initially results in an increase in echo suppression threshold, while for higher cutoff frequencies echo suppression threshold drastically decreases. For broadband direct sound and filtered reflections, the echo suppression threshold is inversely related to high frequency content.

A Single-Channel MVDR Filter for Acoustic Echo Suppression

Acoustic echo suppression techniques for full-duplex communication in low-complexity systems are commonly known to introduce distortion to the desired signal (i.e., near-end speech). Moreover, most traditional echo control techniques typically require accurately detecting the contribution of the near-end speaker to the microphone signal (“double talk”). In this letter, we propose a novel approach to acoustic echo suppression, which aims at extracting the near-end signal using a constraint for minimizing the distortion, and without requiring a double-talk detector.

Interplay of light and collisions in photon echo formation

Situations when a set of resonant radiation pulses can not create photon echo (PE) or stimulated photon echo (SPE) at relatively simple optically allowed transition in a gas are investigated. Some cases when dilution by atomic buffer can imply PE or SPE generation are analyzed. Discovered experimentally mechanisms, amplitudes, and polarization properties of these collision induced PE and collision induced SPE are in agreement with theoretical predictions. Dynamic Stark suppression of photon echo is also studied.

FPGA Design and Performance Evaluation of a Pulse-Based Echo Canceller for DVB-T/H

The main design issues and performance characterization of an echo canceller for digital on-channel repeaters (OCRs) applicable to multiple standards for communications and broadcasting are addressed. In particular, in this paper we focus on a DVB-T/H scenario. The low-complexity channel cancellation technique here described is based on the introduction of a negative feedback loop capable to counterbalance the coupling effects between the OCR antennas (echoes). In the initial phase, locally generated pulse trains are transmitted to estimate the coupling channel between the transmitting and the receiving antennas. This first echo estimation is used to set-up the canceling unit, whose purpose is to generate a properly filtered replica of the repeated DVB-T/H signal compensating the echoes. After the initial set-up of the system, efficient tracking of the echoes can be performed through conventional least mean square (LMS) techniques. After developing a proper theoretical model, we introduce and discuss some important performance figures such as mean rejection ratio (MRR) and echo suppression at nominal position (ESNP). Then, a detailed description of our implementation of the echo canceller on a field programmable gate array (FPGA) board is reported. Finally, the performance of our prototype is evaluated and the measurement results are compared with those derived by the analytical model.

Scattering centers modeling of non-anechoic measurement environments

Abstract. Near-field measurements are established techniques to obtain the far-field radiation pattern of an Antenna Under Test via near-field measurements and subsequent near-field far-field transformation. For measurements acquired in echoic environments, additional post-processing is required to eliminate the effects of multipath signals in the resulting far-field pattern. One of such methods models the measurement environment as a multiple source scenario whereby the collected near-field data is attributed to the AUT and some scattering centers in the vicinity of the AUT. In this way, the contributions of the AUT at the probe can be separated from those of the disturbers during the near-field far-field transformation if the disturber locations are known. In this paper, we present ways of modeling the scattering centers on equivalent surfaces such that echo suppression is possible with only partial or no information about the geometry of the scatterers.

The effect of a pulsed magnetic field on the nuclear spin echo signal in ferrite

A pulsed magnetic field produces shifts of domain walls in a magnetically ordered material (ferrite) and thus affects the nuclear spin echo signal in this material. The suppression and restoration of a response signal have been observed using exciting sequences with pulses of different polarities. The established dependence of the spin echo suppression coefficient on the external constant magnetic field confirms the hypothesis that the observed phenomena are related to the domain walls.

Neural time course of visually enhanced echo suppression.

Auditory spatial perception plays a critical role in day-to-day communication. For instance, listeners utilize acoustic spatial information to segregate individual talkers into distinct auditory "streams" to improve speech intelligibility. However, spatial localization is an exceedingly difficult task in everyday listening environments with numerous distracting echoes from nearby surfaces, such as walls. Listeners' brains overcome this unique challenge by relying on acoustic timing and, quite surprisingly, visual spatial information to suppress short-latency (1-10 ms) echoes through a process known as "the precedence effect" or "echo suppression." In the present study, we employed electroencephalography (EEG) to investigate the neural time course of echo suppression both with and without the aid of coincident visual stimulation in human listeners. We find that echo suppression is a multistage process initialized during the auditory N1 (70-100 ms) and followed by space-specific suppression mechanisms from 150 to 250 ms. Additionally, we find a robust correlate of listeners' spatial perception (i.e., suppressing or not suppressing the echo) over central electrode sites from 300 to 500 ms. Contrary to our hypothesis, vision's powerful contribution to echo suppression occurs late in processing (250-400 ms), suggesting that vision contributes primarily during late sensory or decision making processes. Together, our findings support growing evidence that echo suppression is a slow, progressive mechanism modifiable by visual influences during late sensory and decision making stages. Furthermore, our findings suggest that audiovisual interactions are not limited to early, sensory-level modulations but extend well into late stages of cortical processing.

Stereophonic Acoustic Echo Suppression Based on Wiener Filter in the Short-Time Fourier Transform Domain

An open-loop stereophonic acoustic echo suppression (SAES) method without preprocessing is presented for teleconferencing systems, where the Wiener filter in the short-time Fourier transform (STFT) domain is employed. Instead of identifying the echo path impulse responses with adaptive filters, the proposed algorithm estimates the echo spectra from the stereo signals using two weighting functions. The spectral modification technique originally proposed for noise reduction is adopted to remove the echo from the microphone signal. Moreover, a priori signal-to-echo ratio (SER) based Wiener filter is used as the gain function to achieve a trade-off between musical noise reduction and computational load for real-time operations. Computer simulation shows the effectiveness and the robustness of the proposed method in several different scenarios.

Near-Space Vehicle-Borne SAR With Reflector Antenna for High-Resolution and Wide-Swath Remote Sensing

Near-space is recognized as the atmospheric region from 20 to 100 km above the Earth's surface. Near-space vehicles offer several advantages compared to low earth orbit satellites and airplanes because near-space vehicles are not constrained by orbital mechanics and fuel consumption. These advantages provide potential for future remote sensing applications, but little related work has been published. This paper explains what near-space is and how it should be exploited for remote sensing applications. A near-space vehicle-borne synthetic aperture radar (SAR) with reflector antenna and digital beamforming on receive is proposed for high-resolution and wide-swath (HRWS) remote sensing. The system configuration, signal model, imaging scheme, system performance, and nadir echo suppression are investigated. An example system is conceptually designed, along with its system performance analysis. It is shown that the near-space vehicle-borne SAR with reflector antenna can operate with high flexibility and reconfigurability, thus enabling a satisfactory HRWS remote sensing performance.

Integrated acoustic echo and background noise suppression technique based on soft decision

In this paper, we propose an efficient integrated acoustic echo and noise suppression algorithm using the combined power of acoustic echo and background noise within a soft decision framework. The combined power of the acoustic echo and noise is adopted to the integrated suppression algorithm based on soft decision to address the artifacts such as the nonlinear distortion and the disturbed noise introduced from the conventional methods. Specifically, in the unified frequency domain architecture, the acoustic echo and noise signal are efficiently able to be suppressed through the acoustic echo suppression algorithm based on soft decision without the help of the additional noise reduction technique.

Echolocation vs. echo suppression: influence of the precedence effect on the human-sonar localization of reflective surfaces

Event Abstract Back to Event Echolocation vs. echo suppression: influence of the precedence effect on the human-sonar localization of reflective surfaces Ludwig Wallmeier1*, Nikodemus Geßele1 and Lutz Wiegrebe1 1 Ludwig-Maximilians-Universität München, Graduate School of Systemic Neurosciences, Germany Echolocation is an effective perception-action ability of humans, especially used by blind people. However, the precedence effect predicts a conflict of echo analysis and echo suppression: when localizing sound sources, the human auditory system suppresses spatial information of echoes, but just this information underlies effective echolocation. A common approach to investigate the precedence effect is the arrangement of two sound sources that present a direct sound (lead) and a delayed copy (lag). Several experiments on lag-discrimination suppression have quantified the deterioration of spatial information of the lag produced by the lead. This study investigates the interaction of echolocation and precedence effect in terms of discrimination suppression. Sighted subjects performed two versions of an azimuth-discrimination experiment in virtual acoustic space: In the ‘listening’ version, subjects had to discriminate between positions of a single sound source, the leading, or the lagging of two sources, respectively. In the ‘echolocation’ version, the sound sources were replaced by sound reflectors. Here, subjects evaluated the echoes generated in real time from self-produced vocalizations and thereby discriminated between positions of a single reflector, the leading, or the lagging of two reflectors, respectively. Our results show that sighted subjects can be trained to discriminate reflective surfaces by echolocation with accuracy comparable to sound source localization. In the listening version, the presence of a lagging source impaired lead-discrimination only slightly by a factor of 1.6, while a leading source impaired lag-discrimination considerably by a factor of 8.8. The asymmetry between lead- and lag-discrimination shows a strong influence of the precedence effect, which facilitates localization of the lead at the expense of the lag. In the echolocation version, however, this asymmetry was significantly weaker: lead and lag discrimination deteriorated by a factor of 4.8 and 6.2, respectively. These data indicate that the precedence effect is weakened in an echolocation context. Acknowledgements This study was supported by 'Studienstiftung des deutschen Volkes' and 'Graduate School of Systemic Neurosciences'.

The representation of sound localization cues in the barn owl's inferior colliculus

The barn owl is a well-known model system for studying auditory processing and sound localization. This article reviews the morphological and functional organization, as well as the role of the underlying microcircuits, of the barn owl's inferior colliculus (IC). We focus on the processing of frequency and interaural time (ITD) and level differences (ILD). We first summarize the morphology of the sub-nuclei belonging to the IC and their differentiation by antero- and retrograde labeling and by staining with various antibodies. We then focus on the response properties of neurons in the three major sub-nuclei of IC [core of the central nucleus of the IC (ICCc), lateral shell of the central nucleus of the IC (ICCls), and the external nucleus of the IC (ICX)]. ICCc projects to ICCls, which in turn sends its information to ICX. The responses of neurons in ICCc are sensitive to changes in ITD but not to changes in ILD. The distribution of ITD sensitivity with frequency in ICCc can only partly be explained by optimal coding. We continue with the tuning properties of ICCls neurons, the first station in the midbrain where the ITD and ILD pathways merge after they have split at the level of the cochlear nucleus. The ICCc and ICCls share similar ITD and frequency tuning. By contrast, ICCls shows sigmoidal ILD tuning which is absent in ICCc. Both ICCc and ICCls project to the forebrain, and ICCls also projects to ICX, where space-specific neurons are found. Space-specific neurons exhibit side peak suppression in ITD tuning, bell-shaped ILD tuning, and are broadly tuned to frequency. These neurons respond only to restricted positions of auditory space and form a map of two-dimensional auditory space. Finally, we briefly review major IC features, including multiplication-like computations, correlates of echo suppression, plasticity, and adaptation.

METHOD OF DETECTING A DOUBLE TALK SITUATION FOR A “HANDS-FREE” TELEPHONE DEVICE

The device comprises a microphone for detecting a speech signal from a near speaker, and a loudspeaker for reproducing a speech signal from a remote speaker. The processing for canceling the interfering acoustic echo implements an adaptive linear filtering algorithm. Double talk situations are detected by: evaluating an index representative of the convergence or divergence of the algorithm; assessing a predetermined condition for detecting a double talk situation; and if the condition is satisfied, modifying at least one parameter of the algorithm in response to the detection. The representative index may be the norm of the gradient vector describing the adaptation of the filter from one iteration of the algorithm to the next, the conditions being a comparison between the gradient and a threshold. The parameter that is modified double talk situation may be the adaptation stepsize of the algorithm, and also the gain control of an echo suppression stage.

MRI cortical thickness biomarker predicts AD-like CSF and cognitive decline in normal adults

New preclinical Alzheimer disease (AD) diagnostic criteria have been developed using biomarkers in cognitively normal (CN) adults. We implemented these criteria using an MRI biomarker previously associated with AD dementia, testing the hypothesis that individuals at high risk for preclinical AD would be at elevated risk for cognitive decline. The Alzheimer's Disease Neuroimaging Initiative database was interrogated for CN individuals. MRI data were processed using a published set of a priori regions of interest to derive a single measure known as the AD signature (ADsig). Each individual was classified as ADsig-low (≥ 1 SD below the mean: high risk for preclinical AD), ADsig-average (within 1 SD of mean), or ADsig-high (≥ 1 SD above mean). A 3-year cognitive decline outcome was defined a priori using change in Clinical Dementia Rating sum of boxes and selected neuropsychological measures. Individuals at high risk for preclinical AD were more likely to experience cognitive decline, which developed in 21% compared with 7% of ADsig-average and 0% of ADsig-high groups (p = 0.03). Logistic regression demonstrated that every 1 SD of cortical thinning was associated with a nearly tripled risk of cognitive decline (p = 0.02). Of those for whom baseline CSF data were available, 60% of the high risk for preclinical AD group had CSF characteristics consistent with AD while 36% of the ADsig-average and 19% of the ADsig-high groups had such CSF characteristics (p = 0.1). This approach to the detection of individuals at high risk for preclinical AD-identified in single CN individuals using this quantitative ADsig MRI biomarker-may provide investigators with a population enriched for AD pathobiology and with a relatively high likelihood of imminent cognitive decline consistent with prodromal AD.

Build-Up of the Time Threshold of Perception of a Sound Echo Containing High Frequencies

We report here studies on the effects of build-up in the suppression of acoustic echo for noise bursts with bandwidths of 5–18 kHz and durations of 5, 10, 20, and 100 msec. The signal consisted of two bursts delivered in pairs from two loudspeakers positioned to the right (−45°) and left (+45°) of the midline of the head. The series consisted of 10 pairs of identical bursts delivered at a frequency of 4/sec and one pair delayed by 750 msec. The delays from initiation of the first leading loudspeaker and the second, delayed, loudspeaker in the pairs were 1, 2, 4, 8, 16, 32, 64, and 125 msec. The suppression build-up effect was assessed in terms of the echo threshold, which was determined by reporting the number of sound sources heard. Suppression build-up effects were obtained for all burst durations. However, despite the fact that the mean echo thresholds for all subjects were slightly longer on presentation of the lead signal on the right than on the left, there were no significant differences for signals of durations 5, 10, 20, and 100 msec (p > 0.05).

Adaptation to room acoustics using the modified rhyme test.

The negative effect of reverberant sound energy on speech intelligibility is well documented. Recently, however, prior exposure to room acoustics has been shown to increase intelligibility for a number of listeners in simulated room environments. This room adaptation effect, a possible extension of dynamic echo suppression, has been shown to be specific to reverberant rooms and requires binaural input. Because this effect has been demonstrated only using the Coordinated Response Measure (CRM) corpus it is important to determine whether the increase in intelligibility scores reported previously was due to the specific nature of the CRM task. Here we demonstrate a comparable room-acoustic effect using the Modified Rhyme Test (MRT) corpus in multiple room environments. The results are consistent with the idea that the room adaptation effect may be a natural phenomenon of listening in reverberant environments.

Visual Influences on Echo Suppression

Locating sounds in realistic scenes is challenging because of distracting echoes and coarse spatial acoustic estimates. Fortunately, listeners can improve performance through several compensatory mechanisms. For instance, their brains perceptually suppress short latency (1-10 ms) echoes by constructing a representation of the acoustic environment in a process called the precedence effect. This remarkable ability depends on the spatial and spectral relationship between the first or precedent sound wave and subsequent echoes. In addition to using acoustics alone, the brain also improves sound localization by incorporating spatially precise visual information. Specifically, vision refines auditory spatial receptive fields and can capture auditory perception such that sound is localized toward a coincident visual stimulus. Although visual cues and the precedence effect are each known to improve performance independently, it is not clear whether these mechanisms can cooperate or interfere with each other. Here we demonstrate that echo suppression is enhanced when visual information spatially and temporally coincides with the precedent wave. Conversely, echo suppression is inhibited when vision coincides with the echo. These data show that echo suppression is a fundamentally multisensory process in everyday environments, where vision modulates even this largely automatic auditory mechanism to organize a coherent spatial experience.

Neural time course of visual influence on echo suppression

Event Abstract Back to Event Neural time course of visual influence on echo suppression Lee M. Miller1*, Christopher W. Bishop1 and Sam London1 1 Center for Mind & Brain, University of California at Davis, United States Everyday environments are cluttered with acoustic echoes, which severely impair cognitive processes such as selective attention and spoken communication. Fortunately, the brain copes with this interference by suppressing short-latency (1-10 msec) reverberations – an illusion known as the precedence effect. We have shown behaviorally that in addition to acoustic factors, vision too can profoundly modulate echo suppression. In this study, we identified the time window of vision’s contribution to echo suppression by acquiring 64-channel electroencephalography (EEG) from subjects presented with temporally leading and lagging noise bursts (5.78 +/- 1.70 msec delay). The noise bursts, located in opposite hemifields, were presented either unimodally or paired with a visual flash at the time and place of the leading sound. Subjects reported whether they heard a sound at only the leading location (echo suppression succeeded) or both the leading and lagging locations (echo suppression failed). In agreement with our previous behavioral findings, echo suppression increased in the audiovisual condition compared to the auditory-only condition (p=0.01; mean increase of 10.2 +/- 2.8%). This benefit correlated with EEG activity reflective of a rostrocaudally oriented source from 105-145 msec post stimulus onset (effect averaging 0.48+/-0.11 microvolts in amplitude; p = .009), coincident with the auditory evoked N1 response. These findings refute existing models that advocate exclusive subcortical mediation of echo suppression. They instead show that multisensory cortical mechanisms play an early, critical role in parsing and organizing our perceptual world. Funding: Supported by the NIH/NIDCD R01-DC8171, R01-DC8171-04S1, F31DC011429. Keywords: EEG, Perception Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Poster Sessions: Neurophysiology of Sensation and Perception Citation: Miller LM, Bishop CW and London S (2011). Neural time course of visual influence on echo suppression. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00474 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Nov 2011; Published Online: 28 Nov 2011. * Correspondence: Dr. Lee M Miller, Center for Mind & Brain, University of California at Davis, California, United States, leemiller@ucdavis.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Lee M Miller Christopher W Bishop Sam London Google Lee M Miller Christopher W Bishop Sam London Google Scholar Lee M Miller Christopher W Bishop Sam London PubMed Lee M Miller Christopher W Bishop Sam London Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Is There a Hearing Aid for the Thinking Person?

The history of auditory prosthesis has generally concentrated on bottom-up processing, that is, on audibility. However, a growing interest in top-down processing has focused on correlations between success with a hearing aid and such higher order processing as the patient's intelligence, problem solving and language skills, and the perceived effort of day-to-day listening. Examination of two cases of cognitive effects in hearing that illustrate less-often-studied issues: (1) Individual subjects in a study use different listening strategies, a fact that, if not known to the experimenter, can lead to errors in interpretation; (2) A measure of shared attention can point to otherwise unknown functional effects of an algorithm used in hearing aids. In the two examples described above: (1) Patients with cochlear implants served in a study of the binaural precedence effect, that is, echo suppression. (2) Individuals identifying speech-in-noise benefit from noise reduction (NR) when the criterion was improved performance in simultaneous tests of verbal memory or visual reaction times. Studies of hearing impairment, either in the laboratory or in a fitting session, should include study of the complex stimuli that make up the natural environment, conditions where the thinking auditory brain adopts strategies for dealing with large amounts of input data. In addition to well-known factors that must be included in communication, such things as familiarity, syntax, and semantics, the work here shows that strategic listening can affect even how we deal with seemingly simpler requirements, localizing sounds in a reverberant auditory scene and listening for speech in noise when busy with other cognitive tasks.

Spatial Hearing in Echoic Environments: The Role of the Envelope in Owls

In the precedence effect, sounds emanating directly from the source are localized preferentially over their reflections. Although most studies have focused on the delay between the onset of a sound and its echo, humans still experience the precedence effect when this onset delay is removed. We tested in barn owls the hypothesis that an ongoing delay, equivalent to the onset delay, is discernible from the envelope features of amplitude-modulated stimuli and may be sufficient to evoke this effect. With sound pairs having only envelope cues, owls localized direct sounds preferentially, and neurons in their auditory space-maps discharged more vigorously to them, but only if the sounds were amplitude modulated. Under conditions that yielded the precedence effect, acoustical features known to evoke neuronal discharges were more abundant in the envelopes of the direct sounds than of the echoes, suggesting that specialized neural mechanisms for echo suppression were unnecessary.